Metering and Measurement
Metering is done to determine the amount of electric energy consumption. This note article describes the concept of metering in brief. In addition to that, the two major types of electric meters are also explained in brief. The types of metering process are also explained along with their schematic diagram.
Summary
Metering is done to determine the amount of electric energy consumption. This note article describes the concept of metering in brief. In addition to that, the two major types of electric meters are also explained in brief. The types of metering process are also explained along with their schematic diagram.
Things to Remember
- Metering is done to determine the amount of electric energy consumption.
- There are mainly two types of electric meters: electromechanical type and electronic (digital) type.
- Whole current metering is done for low voltage and low current.
- CT metering is done for low voltage and high values of current.
- HT metering is done for high voltage and current.
MCQs
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Subjective Questions
Q1:
Write a short note on the tongue.
Type: Short Difficulty: Easy
<p>The tongue is a muscular organ in the mouth. The tongue is covered with moist, pink tissue called mucosa. Tiny bumps called papillae give the tongue its rough texture. Thousands of taste buds cover the surfaces of the papillae. Taste buds are collections of nerve-like cells that connect to nerves running into the brain. There are three taste receptors located in the taste bud. They are:</p>
<ul>
<li><strong>Vallate papillae</strong></li>
</ul>
<p>The village papillae are the largest papillae. They are 1-2 mm in diameter and are 8-12 in number. They are situated in the back of the tongue and arranged in the inverted 'V' shape.</p>
<ul>
<li><strong>The fungiform papillae</strong></li>
</ul>
<p>The fungiform papillae are numerous near the tip and margin of the tongue but some of them are also scattered over the dorsum of the tongue. These are smaller than the village papillae but larger than the filiform papillae. They usually appear as pink or red spots.</p>
<ul>
<li><strong>The filiform papillae</strong></li>
</ul>
<p>The filiform papillae are the smallest papillae. They are numerous in number. They are scattered over anterior two-third of the tongue. Although apparently, there are numerous varieties of taste senses, the fundamental taste sensations are only four in number. They are salt, sweet, sour and bitter. The tip of the tongue is very sensitive to the sweet taste, the back to the bitter, the sides are sensitive to sour and salty taste.</p>
<p> </p>
<h4>Mechanism of taste</h4>
<p>The molecules of substances are attached to the molecular receptor of the microvilli in the taste buds. This combination leads to some electrophysiological changes to cause stimulation of receptor cell and then nerve fibres, which emerge from the taste buds, are stimulated. The impulses then reach the appropriate part of the appropriate part of the brain through the various nerves. Then perceived the sense of taste.</p>
<p> </p>
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tongue (human sense organ)
Metering and Measurement
Metering and measurement
Metering, or meter reading, is defined as the act of measuring physical quantities (energy in case of electric power system) with the aid of certain meters or instruments. It can also refer to the datum about some physical state which is obtained by using a meter and some other instruments. Meter reading, in the case of electric power system, is done to determine and record the amount of actual energy consumption by an individual customer over a period of specific time. Generally, meter readings are conducted on a monthly basis or once in two months or once in three months. They may be done either by the utility itself by appointing meter readers or on some contract basis through some contractors.
The amount of electric energy consumed by a user is determined by the utilities with electric meters installed at the consumers' homes. Electric meters are of two types. They are described briefly below.
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Electromechanical type
Electromechanical meters are the conventional type of meters which are commonly used by consumers. They consist of a non-magnetic but electrically conductive disc which rotates proportionally to the power passing through the meter.
An electromechanical meter constantly consumes a small amount of power proportional to the voltage (which is not registered on the meter) and proportional to the amount of current flowing through the meter (which is registered on the meter). The rotating disc is therefore acted upon by two sets of coils which result in the formation of a small two-phase induction motor. The voltage coil produces a magnetic flux in proportion to the voltage and the current coil produces a magnetic flux in proportion to the current. The disc is therefore subjected to a flow of eddy currents and a force is exerted on the disc which is proportional to the instantaneous value of current, voltage and the existing power factor. A permanent magnet serves to act as a brake which exerts a braking force proportional to the speed of rotation of the disc. Therefore, the disc rotates at a constant speed which is proportional to the power flowing through the meter or in other words, the power consumed by the consumer.
Electromechanical meters are cheap but have more moving parts which cause more friction and breakdown of the moving parts. They are also less accurate than the electronic meters. They are used on a single phase AC supply.
2. Electronic type
Electronic or digital type meters are superior to the electromechanical type in terms of functionality, features, and accuracy. However, they are costlier than the electromechanical type meters. The meter usually consists of a power supply, a metering engine, and a processing system. Voltage and current are given as input to the electronic meters along with reference voltage. Some form of sampling and quantizing circuits are also used along with ADCs (Analog to Digital Converters) in order to obtain a digital output. The processed parameters are finally displayed on the LCD or LED screen. These meters also have the feature of data logging in order to store the data for future use.
Metering types
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Low tension metering
Low tension metering is employed for low supply voltages. The voltage level, in this case, is either 230 V (single phase supply) or 400 V (three phase supply). The low tension metering can again be classified into two types which are listed below.
- Whole current metering
This method of metering is employed when the flow of current is small. This is usually the case in households of the consumers and some small business ventures. The KWh meter or the energy meter is directly connected to the system voltage and the current passes through the meter directly. The schematic representation is shown below.
- CT metering
This method is employed when the flow of current is large. This is usually the case in small industries. As shown in the figure below, the energy meter is directly connected to the system voltage while the system current is fed to the energy meter after reducing it with a current transformer.
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High tension metering
This type of metering method is employed when the system voltage is greater than 400 V and the system current is also substantially large. This is usually the case in commercial consumers such as shopping malls, entertainment centers, etc. and industries. The system voltage and current should be reduced before being fed to the energy meter. Therefore, current transformers and potential transformers should be used to reduce the current and voltage respectively. The schematic diagram of the metering method is shown below.
References
- Wikipedia. (2016).Electricity Meter.Retrieved from https://en.wikipedia.org
Information from the class notes and handouts provided by my lecturer Mr. Gopal Joshi Subedi has also been used.
The images were taken from:
Lesson
RE Network Operation
Subject
Electrical Engineering
Grade
Engineering
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